1. Field of the Invention
The present invention relates to an apparatus for measuring the concentration of a gas. Typically, the gas is an exhaust gas, emitted through a stack, produced as a result of combustion.
2. Prior Art
Gas measuring apparatus for monitoring the output of combustion at a stack is well known. For example, one such system is taught in U.S. patent application Ser. No. 422,054 filed Sept. 23, 1982.
Typically such devices operate in a high temperature environment. If the temperature is sufficiently high, various parts of the system can generate electromagnetic radiation in the infrared, visible and ultraviolet ranges called thermal radiation, which can interfere with the system operation.